DS/CDMA with in-cell spreading sequence reuse and iterative multistage detection

We introduce a code-division multiple access (CDMA) concept which makes it possible to accommodate a higher number of users than the spreading factor N. The idea is to assign orthogonal spreading sequences, overlaid with a pseudo-noise (PN) sequence, to the first N users, and to reuse these orthogonal spreading sequences, but overlaying them with another PN sequence for all additional users. The proposed technique can thus accommodate N users without any mutual interference and a number of additional users at the expense of some signal-to-noise ratio (SNR) penalty. This represents a significant capacity increase with respect to presently available multiple access techniques. When the total number of users is larger than N, detection is performed in two separate steps, one for the first N users and one for the set of additional users. Furthermore, the process is iterated two or more times to obtain more reliable receiver decisions